Catheters or cannulas with relatively large diameters are commonly used in various surgical procedures, which include draining fluid from a body cavity, delivering fluid to a body tissue, and introducing surgical and diagnostic tools. To access a body tissue for insertion of these large catheters or cannulas, a guidewire is traditionally used, as described by Seleinger in Br. J 2(6026):21-22 (1976), incorporated herein by reference in its entirety. For example, to insert an internal jugular cannula to provide venous drainage for cardiopulmonary bypass during coronary artery bypass grafting surgery, a patient's right internal jugular vein is first punctured by a small diameter needle. A guidewire is then inserted through the needle into the internal jugular vein. The needle is withdrawn, leaving the guidewire in the blood vessel. A dilator is inserted over the guidewire into the puncture site to enlarge the opening into the internal jugular vein. The dilator is removed and the venous drainage cannula is inserted over the guidewire into the internal jugular vein. After final placement of the cannula, the guidewire is removed, leaving the cannula in the internal jugular vein and available to drain venous blood to a cardiopulmonary bypass machine. In this approach, dilators are used to enlarge an opening on the body tissue for inserting cannulas, and therefore, often traumatize the body tissue.
To reduce the trauma associated with these access devices, thin wall construction using elastomeric materials has been attempted. However, access devices formed of these materials possess a tendency to buckle or bulge during insertion. To overcome the problem of buckling and folding, an adjustable vascular introducer formed of a rolled up plastic sheath in tube form surrounded by a coaxial elastic sheath was described in Cardiovasc. Intervent. Radiol. 2:169-171 (1989), incorporated herein by reference in its entirety. This device would expand around the oversized portion of a balloon catheter as it passed through the device. This adjustable introducer, however, has an expandable circular cross-section which limits its applicability beyond balloon valvuloplasty.
Other introduction devices which utilize a trocar or dilator inside a straight or curved cannula to facilitate insertion of the cannula have been described in Klyce et al., U.S. Pat. No. 4,863,430, incorporated herein by reference. Although these devices simplify the steps for inserting a cannula, they lack the ability to protect the cannula, especially when mounted with fragile, exposed, external balloons, from damage during insertion.
A need therefore exists for an introducer system which provides dilation capabilities to facilitate insertion of a medical device into a body tissue, and provides protection for the device and the body tissue from trauma during insertion.